Purification、Chemical Modification And Biological Activity Of Polysaccharides From Derdrobium Hancockii

The stems of many plants of Dendrobium are used as medicinal herbs,which can regulate immunity and protect liver.Derdrobium hancockii Paxt is a species of medicinal Dendrobium,which can strengthen body.Researches show that polysaccharides are the main active ingredient in medicinal dendrobium.The bioactivities of polysaccharides are considered to be closely related to their molecular weight,space structure,species and content of substituents.The large molecular weight and some special groups of polysaccharides can lead to its low bioactivity.In the present study,in order to obtain polysaccharide derivatives with better biological activity,the structure of polysaccharides from Derdrobium hancockii was identified,the chemical modifications of polysaccharides such as degradation,deacetylation and carboxymethylation were carried out,and their antioxidant and antibacterial activities were compared.The main results are as follows:1.The crude polysaccharide(PDH)was extracted from Derdrobium hancockii by water extraction and alcohol precipitation,and was deproteinized by Sevag.It was purified firstly by column of DEAESepharose Fast Flow and secondly by column chromatography of Sephadex G-200.Finally,three refined polysaccharides were obtained,namely PDH-W-1,PDH-W-2,PDH-S-1.Their molecular weight were analyzed by high-performance gel chomatography as 4.04×104 Da,8.35×103 Da,8.78×106 Da respectively.Their structures were established to be a main chain consisted of partially acetylated mannose linked byβ-(1→4)glycoside bond,and a small amount of glucose by GC,IR and NMR.The main difference of three refined polysaccharides was the length of the chain.2.PDH was degraded by ascorbic acid in combination with H2O2 to offer degraded polysaccharide(DGPDH).The optimum degradation conditions were obtained by RSM as follows:concentration of H2O2 and Vc 20 mM/L,reaction time 1.6 h,and temperature 45.7℃.The rate of scavenging DPPH radical was 30.02%at 0.4 mg/mL of DGPDH obtained by these conditions.3.The acetyl group of PDH was removed by thermal alkali to offer deacetylated polysaccharide(DAPDH).The optimum deacetylated conditions were obtained by RSM as follows:concentration of NaOH 1.0 mol/L,reaction time 2.5 h,and temperature 73.3℃.The rate of scavenging DPPH radical at 0.2 mg/mL of DAPDH obtained by the optimum conditions was 54.05%.4.Carboxymethylated polysaccharide(CPDH)was obtained from PDH modified with alkaline chloroacetic acid.The effect of modification was checked by IR.5.In vitro antioxidant activity of PDH,PDH-W-1,PDH-W-2,PDH-S-1,CPDH,DGPDH,DAPDH was evaluated by determining their radical(DPPH,ABTS)scavenging ability,and ferric iron reducing ability.The results showed that the antioxidant activities of DAPDH and DGPDH were higher than that of PDH,but the antioxidant activities of CPDH,PDH-W-1,PDH-W-2,PDH-S-1 were decreased compared with that of PDH.6.Escherichia coli,Bacillus subtilis,Salmonella,Bacillus cereus,Salmonella pullorum was selected as the tested strains.In vitro antimicrobial activities of all polysaccharides on the tested strains were evaluated by the minimum inhibition concentrations(MIC)values.The results demonstrated that DAPDH(MIC:5、2.5、5、5、5 mg/mL),DGPDH(NIC:5、5、10、5、10 mg/mL),PDH-S-1(MIC:10、10、10、5、10 mg/mL)had marked inhibitory effect on the five strains.The PDH,PDH-W-1,PDH-W-2 and CPDH had no obvious inhibitory action.